Field of the Invention
The present invention relates to an apparatus and a method for controlling a tunnel current flowing between a first conductive object and a second conductive object.
Related Background Art
Non-Patent Document 1 describes that a tunnel current flows between a tip of a probe and an observation object by focusing a terahertz wave pulse in a gap between the tip of the probe and the observation object in a scanning tunneling microscope (STM). When utilizing this technique, it is possible to cause a tunnel current to flow between the tip of the probe and the observation object by focusing the terahertz wave pulse into the gap between the tip of the probe and the observation object in addition to or in place of applying a voltage between the probe and the observation object as in the conventional STM, further, it is possible to observe a structure of a surface of the observation object when the tunnel current is measured by scanning the probe relative to the observation object. Such an STM is referred to as a THz-STM.
Non-Patent Document 2 describes that a magnitude and a direction of a tunnel current flowing when a terahertz wave pulse is focused in a gap between a tip of a probe and an observation object are dependent on a carrier envelope phase (CEP) of the terahertz wave pulse. In this document, the CEP of the terahertz wave pulse is changed by inserting a pair of spherical lenses or a pair of cylindrical lenses on an optical path of the terahertz wave pulse. That is, with reference to the CEP of the terahertz wave pulse when the pair of spherical lenses and the pair of cylindrical lenses are not inserted, the CEP of the terahertz wave pulse is shifted by π/2 by inserting the pair of cylindrical lenses, and further, the CEP of the terahertz wave pulse is shifted by it by inserting the pair of spherical lenses.
Here, a terahertz wave is an electromagnetic wave having a frequency of about 0.01 THz to 100 THz corresponding to an intermediate region between a light wave and a radio wave, and has an intermediate property between the light wave and the radio wave. Further, the CEP indicates a relation of a phase of an electric field oscillation (carrier) in a light pulse with respect to a shape (envelope) of a temporal change of an amplitude of the light pulse in techniques utilizing ultrashort pulses such as femtosecond laser light pulses and terahertz wave pulses. A CEP of a light pulse of linearly polarized light is defined by a phase of an electric field at a peak position of an amplitude of the light pulse. Further, a CEP of a light pulse of circularly polarized light can be defined by a direction of an electric field vector at a peak position of an amplitude of the light pulse.
When utilizing the generation of the tunnel current caused by focusing the terahertz wave pulse, it is expected that time-resolved measurement of single molecular vibration becomes possible, and further, it is also expected that verification of a screening effect in semiconductors becomes possible. In addition, when utilizing the fact that the magnitude and the direction of the tunnel current in an extremely minute region can be controlled at an extremely high speed, it is expected to realize an electronic device such as a transistor using ultra-high-speed electronic control, for example, and an application such as precision processing of a minute region is also expected.
Non-Patent Document 1: T. L. Cocker, et al., “An ultrafast terahertz scanning tunnelling microscope”, Nat. Photon. Vol. 7, pp. 620-625 (2013)
Non-Patent Document 2: K. Yoshioka, et al., “Real-space coherent manipulation of electrons in a single tunnel junction by single-cycle terahertz electric fields”, Nat. Photon. Vol. 10, pp. 762-765 (2016)